The invention relates to spin valve sensors for use in magnetic disc read/write heads.
Magnetic sensors utilizing giant magnetoresistance (GMR) effects have utility as magnetic sensors, especially in magnetoresistive read heads used in magnetic disc storage systems. The GMR effect is observed in ultrathin, electrically conductive multilayer systems having magnetic layers. Magnetic sensors utilizing the GMR effect are frequently referred to as "spin valve" sensors.
A spin valve sensor is typically a sandwiched structure including two ferromagnetic layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers is called the "pinned layer" because it is magnetically pinned or oriented in a fixed and unchanging direction. One common method of maintaining the magnetic orientation of the pinning layer is through anti-ferromagnetic exchange coupling utilizing a proximate, i.e. adjacent or nearby, anti-ferromagnetic layer, commonly referred to as the "pinning layer." The other ferromagnetic layer is called the "free" or "unpinned" layer because its magnetization can rotate in response to the presence of external magnetic fields.
The benefits of spin valve sensors result from a large difference in electrical conductivity exhibited by the devices depending on the relative alignment between the magnetizations of the two ferromagnetic layers. In order for antiferromagnetially pinned spin valve sensors to function effectively, a sufficient pinning field from the pinning layer is required to keep the pinned ferromagnetic layer's magnetization unchanged during operation. Various anti-ferromagnetic materials, such as NiMn, FeMn, NiO, IrMn, PtPdMn, CrMnPt, RuRhMn, and TbCo, have been used or proposed as antiferromagnetic pinning layers for spin valve sensors